Method of manufacturing steel sheets



UNITED;sTArE'S *o'r'r'o Henson cunnmeneia, or BRACKENRIDGE, PENNSYLVANIA; assienoa To. saacksniunea, PENNSYLVANIA, A COR-' 1 ZVALLEY HoLnrNecoRPoRA'rIoN; or

" PORATI ONOF PENNSYLVANIA.

, f. M'ErHonor ivtannrnernnnvesrsnr. Seam I Kareem; I

To aZZcvhom it may concern:

Be it known thatjI, OTTO HERRON (JU N Ne'i-rA ai, a'citizen of'the United States and a resident of'flB'rackenridge. in the county of Allegheny and the State of Pennsylvania,

havemade anew and useful Invention in Method' of Manufacturing Steel Sheets, of

which the following is a specification.

This invention relates to the manufacture of steel sheets and j particularly to sheets capable of meeting the requirements of the.

automobile and metal furniture trade where difiicult stamping operations are encountered andywhere a high surface finish is necessary.

An object of-thi's invention is to provide a method whereby low carbon steel sheets having a highly finished surface and suitable for deep stamping operations can be uniformly produced at a relatively low cost.

Another object of this invention is to provide a method whereby low carbon steel in lengths correspondlng to the width of sheets having a highly finished surface and free from Steads brittleness can be produced at a relatively low cost.

a A further object of this invention is to provide a method whereby steel sheets of uniform quality and free from Steads brittleness and having a highly finished surface can be produced at a relatively low cost.

In the standard commercial methods of producing what are now known as high grade sheets for said trades, the ingots are first rolled into sheet barswhich are cut up the sheets to be produced. The sheet bars are heated and roughed down in a two high mill to a definite length which length is determined by the final length of the sheet required. The roughed down sheets are then matched or paired, reheated and finished to length and gauge.

In thisprocess,, the number of sheets rolled in one pack and the number of times heatedare determined by the final gauge and length, of the sheet and the final length and gauge produced in the hot mill is approximately the final length and gauge of the finished sheet.

In order to obtain the surface finish necessary in these trades. the sheets, after being hot rolled, are pickled to remove the scale, then cold rolled to give the desired surface PATENTQ'OFFICE iip ieaeoaaa' oa ber 13.1324. Serial Maggie, j j

and then annealed"to remoye stisfiessandi strains.

It is extremelyimportant that these sheets, i i

:be properly annealedto adaptthem'to 'dif-' ficult stamping operations, but the annealing of these cold rolledand highly finished sheets is rendereddifiieult' beeause"of the H phenomenon known as Steads brittleness Stick or weld together if box-annealed at r normalizing temperature.

This phenomenon manifests itself in a growth of the ferrite crystals which causes the sheets to become extremely brittle.

It is Well known that Steads brittleness can be corrected by increasing the temperature of the anneal or increasing the reduction made during cold rolling. It is impossible to increase the anneal in the ordinary sheet process to a temperature sufit ciently high to eliminate Steads brittleness for the reason that at this temperature, which is in the neighborhood of 1650 F. the sheets will stick or weld together in the standard commercial box anneal process.

It has been shown by various researches that if low carbon steel is subjected to cold roll reduction in excess of 10 per cent,

Steads brittleness will not occur, even though the steel is annealed at a temperature below the normalizing temperature of 1650 F. ,This knowledge has, so far as I know, never been utilized in the manufacture of high grade sheets. The work done on the cold rolls has been confined merely to improving the surface and has not been sufficient to eliminate the strains that produce recrystallization during annealing.

In the regular commercial processes with which I am familiar, after the sheets have been hot rolled it is customary to anneal in some cases up to ,the normalizing temperature to pickle and then to cold roll in one, two or three passes Wlth a total cold roll reduction that rarely exceeds 5 per] cent. After the cold rolling, the sheets are reannealed at a lowtemperature made neces sary in order to prevent sticking of the smooth polished.surfaces.

'So far as I know, whenever hot rolled sheets have been cold rolled in order to improve or obtain the surface finish required in the a tomobile, metal furniture and other trades, hen similar sheets are required, the cold rolling has invariably resulted in crystallization of the ferrite structure and consequently has produced brittle sheets.

In carrying out this method, sheet bars of the proper \length and gauge are produced according to standard practice. The sheet bars are then hot rolled according to standard practice to a length considerably less than the length of the sheet required or to be more definite, to a length which will require a reduction of at least 10 per cent of the total reduction (the reduction from the gauge of the sheet bar to the gauge of the finished sheet) to bring the sheet to the final-length and gauge required.

The semi-finished sheets are then annealed or normalized at a temperature of from 1600 F. to 1700 F. The normalized sheets are then pickled to remove the scale and are then cold rolled to length.

The cold rolled sheets are then reannealed at a relatively low temperature in order to prevent sticking or welding. Low temperature annealing can be utilized since recrystallization will not occur due to the cold roll reduction of 'at least 10 per cent.

The cold rolled reduction of at least 10 per cent is preferably obtained in one pass, althoughI find that satisfactory results can be obtained if two or more passes are used.

I have found that instead of normalizing the semi-finished sheets, satisfactory results can be obtained, especially when rolling sheets of heavy gauge, if the sheets are brought to the semi-finished gauge (that is,

, the gauge where hot rolling ceases and cold rolling begins) in the hot mill at a normalizing temperature. That is, if the sheets are discharged from the hot mill at a normalizing temperature and thereafter pickled, cold rolled and reannealed as above described. 0

I find that sheets made in accordance with this method are uniform as to drawing and stamping qualities and due to the cold rolling have a highly finished surface such as required in the trades referred to.

Having thus described my invention, what I claim is 1. The method, which consists in hot rolling steel sheets to a size considerably less and a gauge considerably greater than'the'f size and gauge of the finished sheets, 1n-

then annealing the sheets at a normalizing temperature, in then pickling the sheets to remove the scale, in then cold rolling the sheets to length and gauge and then in annealing the sheets at a temperature below the normalizing tem rature.

2. The method, which consists in hot rolling steel sheets to a gauge which is at least 10 per cent greater than the gauge of the finished sheets, in then annealing the sheets at normalizing temperature, in then pickling the sheets to remove the scale, in then cold rolling the sheets to length and gauge and then in annealing the sheets whereby sheets of uniform quality having highl finished surfaces and free from Steads rittleness are obtained.

3. The method, which consists in hot rolling sheets to a size considerably less than the size of the sheets required, in then annealing the sheets at normalizing temper-' ature, in then pickling the normalized sheets to remove the scale, in then coldrolling the pickled sheets to length and gauge and then in box annealing the sheets.

4. The method, which consists in hot roll- 1 ing sheets to a size considerably less than the size of the sheets required, in then annealing the sheets at normalizing temperature, in then pickling the normalized sheets to remove the scale, in then cold rolling the pickled sheets to length and gauge and then in box annealing the sheets at a term perature below normalizing temperature.

5. The method, which consists in hot rolling sheets to a gauge which is at least 10 per cent greater than the gauge of the finished sheets, in then annealing the sheets at a normalizing temperature, in then pickling the sheets to remove the scale, in then cold rolling the sheets to length and gauge and then in box annealing the sheets whereby sheets of uniform qua'lity having highly polished surfaces and free from Steads brittleness are obtained.

6. The method, which consists in hot rolling sheets and irdischarging them from the hot mill at normalizing temperature and of a size considerably less and a gauge considerabl greater than the size and gauge of the Iihished sheets, in then pickling the sheets to remove the scale, in then cold rolling the sheets to length and gauge and then in annealing the sheets at a temperature below normalizing temperature.

7. The method, which consists in hot rolling steel sheets and in discharging the sheets from the hot mill at normalizing temperature and of a gauge which is at least 10 per cent greater than the gauge of the finished sheets, in then pickling the sheets to remove the scale, in then cold rolling the sheets and then in annealing the sheets.

In testimony whereof, I have hereunto subicribed my name this 8th day of October, 192

OTTO HERRON CUNNINGHAM. 

